The incorporation of electronic devices within pneumatic tyres is taking a greater importance in order to increase safety of vehicles. Tyre electronics may include sensors and other components suitable for obtaining information regarding the behavior of a tyre, as well as various physical parameters thereof, such as for example temperature, pressure, number of tyre revolutions, vehicle speed, etc. Such information may become useful in tyre monitoring and/or alarm systems. Furthermore, active control systems of the vehicle may be based on information sent from sensor devices included within the tyres.
Integrated tyre electronics systems have conventionally been powered by a variety of techniques and different power generation systems.
A typical solution for powering tyre electronics systems is the use of a non-rechargeable battery, which may cause inconveniences to a tyre user since proper electronics system operation is dependent on periodic battery replacement. As a matter of fact, batteries tend to deplete their energy storage quite rapidly when powering electronic applications characterized by complex levels of functionality. Furthermore, conventional batteries typically contain heavy metals that are not environmentally friendly and which present disposal concerns. Moreover, performances of conventional batteries are often influenced by temperature: in particular, the functioning of such batteries is not reliable at low temperatures.
Another known method for powering tyre monitoring systems is a coupling of radio-frequency (RF) power between an antenna disposed on the vehicle in close proximity with another antenna included within the electronic device disposed in the tyre. This typically requires antennas disposed in vehicle portions frequently exposed to damage from road hazards, and thus may lead to many drawbacks.
The use of energy scavenging or harvesting elements, e.g. based on piezoelectricity, has also been proposed for powering tyre monitoring systems. Piezoelectricity is a property of certain materials, such as quartz, Rochelle salt, and certain solid-solution ceramic materials such as lead-zirconate-titanate (PZT), of generating electrical charge when mechanically stressed.
For example, WO 2005/067073 discloses a tyre comprising a piezoelectric flexing element associated with an energy storage device (e.g. a capacitor). The piezoelectric flexing element is mounted in cantilever fashion in a housing so as to be positioned substantially along a plane orthogonal to a radial direction of said tyre and, so that a first end of the piezoelectric element is restrained to the housing. A loading mass is coupled to the second end of the piezoelectric flexing element. A small gap is formed between the inner walls of the housing and the outer surface of the loading mass, in order to allow limited flexure of the piezoelectric element. The housing including the piezoelectric element is mounted in a tyre portion in correspondence of a tread area of the tyre, preferably on the inner surface of the tyre. The piezoelectric element flexes under the action of the radial acceleration when the tyre rotates. The loading mass and the gap are chosen to obtain: a) small entity oscillations of the flexure element substantially during a complete revolution of the tyre, when the tyre rotates at low speed; b) large entity oscillations of the flexure element substantially only during the passage of the tyre portion including the piezoelectric element in the contact patch.
Typically, wireless transmission is employed in order to send tyre performance information outside the tyre, to a receiver disposed on the vehicle body, so that electronic devices disposed within a wheel typically include a transmitter associated to an antenna.
EP 1484200 relates to a communication system for communicating between a tire/wheel assembly and a vehicle body, which is provided with a wheel-side communication device mounted to the wheel and which rotates together with the wheel, and a body-side communication device mounted in a fixed position to the vehicle body. Communication takes place between the wheel-side communication device and the body-side communication device according to the rotational position of the wheel. According to EP 1484200, when one of the wheel-side communication device and the body-side communication device receives a signal from the other, the reception changes cyclically as the wheel rotates. There is a pattern between the change in that reception and the change in the rotational position of the wheel, in which the reception improves when the actual rotational position of the wheel matches a specific rotational position. The system disclosed in EP 1484200 selectively performs communication between the wheel-side communication device and the body-side communication device at a rotational position of a wheel, from among a plurality of rotational positions of the wheel, with the exception of a rotational position where the communication state between the communication devices may be poor. Moreover, the communication system of EP 1484200 may also be provided with: i) a rotational position detecting device that detects a rotational position of the tire/wheel assembly; and ii) a transmission timing determining device that determines a communication timing based on the relationship between the rotational position of the wheel detected by the rotational position detecting device and a received signal level, which is the level of a signal received from one of the body-side communication device and the wheel-side communication device by the other.
In another document, namely EP 1536392, the object of performing a stable function of the system and of increasing the probability of the transmission and reception even in the presence of a dead point, i.e. a point at which the receive intensity does not reach the receive limit, is said to be achieved by a wheel condition monitoring system having a transmitter which is installed on an individual rotatable wheel to transmit a condition of the wheel and a receiver which is installed on the vehicle body side to receive the condition of the wheel sent from the transmitter, wherein the rotation speed of the wheel is detected (e.g. with an accelerometer), and data indicating the condition of the wheel are sent from the transmitter to the receiver at intervals in accordance with the detected rotation speed of wheel. In particular, the system is configured so that transmission is achieved at intervals corresponding to the rotation speed of wheel. Therefore, even if a dead point at which transmission and reception are impossible is present, the probability that transmission and reception can be accomplished by several times of transmission can be increased, and the system can perform its functions stably. More in detail, when the receiver receives a plurality of pieces of data sent from the transmitter installed on each of a plurality of wheels, first data transmission from the transmitter is performed after each waiting time set for each transmitter has elapsed, so that a problem of transmission overlaps with the transmission of electric waves from another wheel in terms of time, can be overcome.
EP1826029 discloses a system in which acquired wheel information, such as temperature data and inflation pressure data, is surely transmitted from a transmitter in a status where the transmitter is not located in a dead space, by controlling timing wherein the transmitter acquires the wheel information, a transmission time width and transmitting timing of the data to be transmitted from the transmitter by radio. In particular, the wheel information acquiring system disclosed in EP 1826029 acquires wheel information of the wheel during rotation, and comprises:                a first communication device that is attached to the wheel and detects wheel information associated with the wheel during rotation, and wirelessly transmits the detected wheel information from a wheel side; and        a second communication device that is provided apart from the wheel and that receives and acquires the wheel information transmitted by the first communication device,wherein the first communication device has a maximum value of rotation speed specified for the wheel during rotation to which the first communication device is attached (e.g. comprised in a range between 90 km/h and 300 km/h); and wherein when a transmission time width of one packet of the wheel information transmitted by the first communication device is represented by T1, and an expected minimum rotation period-which is determined according to the maximum value of the rotation speed prespecified in the first communication device is represented by R1, T1 is set so as to satisfy T1≦R1·½, preferably T1≦R1· 1/12.        
WO2004/030950 discloses a telemetry unit provided for mounting inside a pneumatic tyre, which includes a piezoelectric element supported in a housing, with an actuator arranged for contact with the element, to deflect the element in response to external forces acting on the actuator during rotation of the tyre. For every rotation of the tyre, cyclic pulses of electrical charge are generated by the deflection of the element. The charge is stored and utilized under a power consumption protocol including the steps of: initiating power to a data measurement circuit for measuring data from the environment local to the unit; disabling power to the data measurement circuit; initiating power to a data transmission circuit; transmitting data from the measurement circuit; and disabling power to the transmission circuit. The power consumption protocol therefore minimizes consumption of the generated power, during measurement and transmission of data by the unit.
EP 1487682 discloses a method for monitoring the behavior of a tyre during running, the method comprising the steps of: acquiring and storing, at least temporarily, a first curve representing the acceleration profile of a first point of the tread area of said tyre, located on a meridian plane of said tyre; acquiring and storing, at least temporarily, at least a second curve representing the acceleration profile of a second point of the tread area of said tyre, located substantially on said meridian plane; comparing said first and second curves, or parameters derived thereof; determining the behavior of said tyre from said comparison.
EP 1676112 discloses a method and a system for determining a cornering angle of a tyre fitted on a vehicle during a running of said vehicle on a rolling surface. The method comprises the steps of: estimating a length of a contact region between said tyre and said rolling surface, said length being measured at a distance from the equatorial plane of the tyre; estimating a load exerted on said tyre; estimating a camber angle to which said tyre is subjected; and deriving such cornering angle from said camber angle, tyre load and contact region length.
EP 1794007 discloses a method and a system for determining a cornering angle of a tyre fitted on a vehicle during a running of said vehicle on a rolling surface. The method comprises the steps of: determining the lateral acceleration of a portion of the tyre tread spaced apart from the equatorial plane of said tyre; determining a rotation speed of said tyre; and determining said cornering angle from said lateral acceleration and said rotation speed, by using characteristic curves of lateral acceleration amplitude versus predetermined values of cornering angle for at least one rotation speed.